Method and memory circuit for operating a resistive memory cell

Abstract

The invention relates to a method for reading a memory datum from a resistive memory cell comprising a selection transistor which is addressable via a control value, the method comprising detecting a cell current flowing through the resistive memory cell, setting the control value depending on the detected cell current, and providing an information associated to the control value as a memory datum.

1. A method for reading data stored in a resistive memory element, the method comprising:
 detecting a cell current flowing through the resistive memory element, wherein the resistive memory element comprises a controllable selection transistor which is controlled by a control value; 
 setting the control value based on the detected cell current; and 
 providing the data depending on the set control value. 
 
     
     
       2. The method of  claim 1 , wherein the detecting of the cell current flowing through the resistive memory element comprises comparing the cell current with a reference current, and wherein the control value is set based on a result of the comparing. 
     
     
       3. The method of  claim 2 , wherein the control value is set such that the cell current substantially equals the reference current. 
     
     
       4. The method of  claim 3 , wherein setting the control value comprises:
 applying a measuring value to the selection transistor; and 
 changing the applied measuring value until a sign of a difference between the cell current and the reference current changes, wherein the measuring value at which the sign of the difference changes is set as the control value. 
 
     
     
       5. The method of  claim 4 , wherein the measuring value is changed by discrete values. 
     
     
       6. The method of  claim 5 , wherein the measuring value is selected from a plurality of different values, and wherein, when the sign of the difference between the cell current and the reference current changes between successively applied measuring values, a last-applied measuring value is set as the control value. 
     
     
       7. The method of  claim 6 , wherein the plurality of different values of the control value corresponds to a number of predetermined resistance states of the resistive memory cell to be detected diminished by one. 
     
     
       8. A memory circuit for reading stored data, comprising:
 a selection transistor which is controlled by a control value, 
 a resistive memory element which is set to a resistance state; and 
 a read unit configured to detect a cell current flowing through the resistive memory element, to set the control value depending on the detected cell current and to provide the data depending on the control value. 
 
     
     
       9. The memory circuit of  claim 8 , wherein the read unit comprises:
 a comparing unit for compare the cell current flowing through the resistive memory cell to a reference current; and 
 a control unit for setting the control value depending on the result of the comparison. 
 
     
     
       10. The memory circuit of  claim 9 , wherein the control unit is configured to set the control value such that the cell current substantially equals the reference current. 
     
     
       11. The memory circuit of  claim 10 , wherein the control unit comprises:
 a measuring circuit configured to apply a measuring value to the selection transistor and to change the measuring value until the comparing unit detects that a sign of a difference between the cell current and the reference current has changed, wherein the comparing unit causes the control unit to set the measuring value at which the sign of the difference has changed as the control value. 
 
     
     
       12. The memory circuit of  claim 11 , wherein the measuring circuit changes the measuring value by discrete values. 
     
     
       13. The memory circuit of  claim 12 , wherein the measuring circuit selects the measuring value from a plurality of different values, and wherein the control unit sets a last-applied measuring value as the control value when the sign of a difference between the cell current and the reference current changes between successively applied measuring values. 
     
     
       14. The memory circuit of  claim 13 , wherein the plurality of different values of the control value corresponds to a number of resistance states of the resistive memory element to be detected diminished by one.